Venous blood sample

Most HIV tests use a blood sample that is taken from a vein in the arm, and this is called venous blood. Venepuncture (a term which means 'puncturing the vein') is the procedure used to obtain the sample. For most people, venepuncture is quick, easy, and relatively painless.

A needle is inserted through the skin into a vein. A small amount of blood is withdrawn through the needle into a tube, which is sent to a laboratory for analysis.

The nurse (or other healthcare professional performing the venepuncture) is usually able to identify a vein in the crook of the elbow that will be easily accessible and applies a tourniquet above the site to make the vein more apparent. Clenching the fist also helps make the vein more prominent. When the needle is inserted under the skin, the patient may feel a slight sting, and there may be additional discomfort when it is withdrawn. Afterward, the patient is asked to apply gentle pressure, over a clean dressing, to help the blood clot and prevent swelling and bruising.

Some tips for people who find venepuncture stressful or uncomfortable:

• Rub or tap the area where the needle will go.
• Establish a slow and steady breathing pattern, and then quietly blow out as you feel the needle being placed.
• Close your eyes and visualise a colour or scene.
• If you are likely to feel woozy or faint, tell the nurse in advance. The blood can be taken while you are lying down, which will help avoid fainting and injury.

Tests may be conducted on whole blood, plasma or serum.

After whole blood has been separated into its liquid and solid components, the clear fluid part is known as plasma. After plasma has been allowed to clot, the remainder is known as serum. Serum and plasma samples can be refrigerated or frozen. Whole blood samples can be refrigerated, but not frozen.